Bob Bidonde
Well-known member
My Model "A" is equipped with a Nu-Rex 12V negative ground 60Amp alternator. I suspect that it is not charging the car's battery as it normally did. How can this alternator's output be checked?
Suspect Alternator
- Thread starter Bob Bidonde
- Start date
Will N
Well-known member
You got a multimeter? Set it to DC voltage, touch the negative lead to the terminal on the starter switch and the positive lead to ground while the engine is running. The alternator should be putting out at least 14v. If you're getting less than than, the alternator isn't charging. (And I suspect you already know this Bob, but you put this out there as a quiz.)
Phil Brown
Well-known member
Bob's neg. ground so he should revirse the leads, ground the neg. and positive to the terminal on the starter switch. Can also check right at the battery terminal's as well, positive to positive and negitive to negitive
nkaminar
Well-known member
I advise to add a voltmeter to your car's instruments. Keep the ammeter. When you first start the car the ammeter should show a charge. As the battery recovers from starting the car the ammeter should go to zero but the voltmeter should show 14 volts. The ammeter alone is not enough to keep track of the battery and alternator health.
Kurt in NJ
Well-known member
I many times will start with the finger test.
If I can take one finger and push on the alternator fan and turn the alternator and the pulley slips on the belt I know the alternator won’t be able to make full output.
For full output testing you need ammeter in the circuit and carbon pile load tester — apply load to bring voltage down to 11.5-12 Volts and raise engine rpm
to test max voltage a 1/4 ohm resistor is placed in series between battery and alternator to simulate full charged battery.
your 60 amp alternator is probably rated 60 amps cold and after 30 seconds of that full output it will drop probably 20% as it warms up —- if the belt can transmit the hp without the belt slipping ( see finger test)
If I can take one finger and push on the alternator fan and turn the alternator and the pulley slips on the belt I know the alternator won’t be able to make full output.
For full output testing you need ammeter in the circuit and carbon pile load tester — apply load to bring voltage down to 11.5-12 Volts and raise engine rpm
to test max voltage a 1/4 ohm resistor is placed in series between battery and alternator to simulate full charged battery.
your 60 amp alternator is probably rated 60 amps cold and after 30 seconds of that full output it will drop probably 20% as it warms up —- if the belt can transmit the hp without the belt slipping ( see finger test)
Herb Concord Ca
Well-known member
Another quick test. With engine off, measure battery voltage at the posts, note reading. Start engine and check alternator output, reading should be higher than the battery voltage you measured in step 1. Typically, an alternator will put out 14 Volts.
BRENT in 10-uh-C
Well-known member
The quickest way I know to check an alternator while out on the road (-or in the driveway) is to touch a screwdriver to the welch plug on the backside of the alternator case (-behind the end of the stator). If it is charging, there will be magnetism to draw the screwdriver to the welch plug. The greater the charge rate, the greater the magnetism. No magnetism, = no charge.
Will N
Well-known member
Don't do that on a car with an original generator!!! The battery is the voltage regulator in an original generator system. The voltage output of the generator will spike without the battery to regulate it, likely burning out the generator in the process.
Bob Bidonde
Well-known member
Will, you are right. I want to know what others do just in case there is a better way. It turns out that the battery in my car was deeply discharged. After using a battery charger for a few hours, the alternator behavior went back to normal. I did not give the alternator enough time to restore the battery.
Big hammer
Well-known member
FYI instructions that came with a new alternator said a dead battery can kill an alternator, charge your battery before attempting to start a car !
Kurt in NJ
Well-known member
With a discharged battery the alternator should have been charging at least 40 amps if it is good and there is no belt slippage.
Perhaps a proper output test should be performed.
I once had a dead battery from leaving the ignition on . I was late for a show and hand crank started my car and after a 20 minute drive the battery was charged enough to start the car— that is with the original generator.
Perhaps a proper output test should be performed.
I once had a dead battery from leaving the ignition on . I was late for a show and hand crank started my car and after a 20 minute drive the battery was charged enough to start the car— that is with the original generator.
Last edited:
BRENT in 10-uh-C
Well-known member
Kurt, definitely not disputing your experiences with that, so I will say that is impressive to think hand cranking provided enough electricity to a dead battery to power an ignition coil enough to create combustion. My experiences has always been that a push start or tow was necessary to require the engine to be spinning for at least several hundred feet to accomplish enough electricity from a Generator to start the engine. Kudos again to you!!
alexiskai
Well-known member
Kurt in NJ
Well-known member
Using a diode cutout the voltage doesn’t have to break the over 6V threshold to close contact.
Ok if you consider 0.01v mostly dead.— so I guess it wasn’t totally dead.
I do have a generator third brush setting that most don’t use—14 amps so I can take long drives at night without daylight driving to charge the battery ( still testing the limits of what I was told would be a temporary repair done 50 years ago)
With that third brush setting there was a peak voltage of 4.5V with a vigorous pull of the crank — enough to make spark.
I just rebuilt a model T generator and since it has a gear I wasn’t going to damage the special belt on the testing machine so I wrapped a string on the gear and pulling that with the third brush at maximum it would close the cutout and peg the analog meter at 10V—- how fast did I spin it I don’t know— probably slower than running down the road but somewhat faster than hand cranking.
the picture is my charge rate with parking lights on.
Ok if you consider 0.01v mostly dead.— so I guess it wasn’t totally dead.
I do have a generator third brush setting that most don’t use—14 amps so I can take long drives at night without daylight driving to charge the battery ( still testing the limits of what I was told would be a temporary repair done 50 years ago)
With that third brush setting there was a peak voltage of 4.5V with a vigorous pull of the crank — enough to make spark.
I just rebuilt a model T generator and since it has a gear I wasn’t going to damage the special belt on the testing machine so I wrapped a string on the gear and pulling that with the third brush at maximum it would close the cutout and peg the analog meter at 10V—- how fast did I spin it I don’t know— probably slower than running down the road but somewhat faster than hand cranking.
the picture is my charge rate with parking lights on.
Attachments
Last edited:
rotorwrench
Well-known member
Bad batteries aren't good for any type of electrical power generation device. The three brush generators are the most vulnerable since system voltage it regulated by the battery.
If the Nu-Rex is a 10si that I'm familiar with, then it is a fairly reliable alternator for 12-volt systems. They work better if they have a generator warning light wired in as was the original GM design in order to have automatic output excitement. If it's a single wire then the engine rpm has to be brought up in order to excite the alternator start. I've had one on my 1956 Ford 850 tractor for a long time and it works very well with little or no trouble other than insuring belt tension. I wish the 6-volt positive ground ones were as reliable but they aren't quite there yet. The internal regulators tend to overcharge the battery.
Nu-Rex has their own pulley and internal components to some degree.
If the Nu-Rex is a 10si that I'm familiar with, then it is a fairly reliable alternator for 12-volt systems. They work better if they have a generator warning light wired in as was the original GM design in order to have automatic output excitement. If it's a single wire then the engine rpm has to be brought up in order to excite the alternator start. I've had one on my 1956 Ford 850 tractor for a long time and it works very well with little or no trouble other than insuring belt tension. I wish the 6-volt positive ground ones were as reliable but they aren't quite there yet. The internal regulators tend to overcharge the battery.
Nu-Rex has their own pulley and internal components to some degree.
Big hammer
Well-known member
One day after school I was asked to give a friend a ride home, dead or low battery as it turned over once . My rider got help to push the car in the flat parking lot, I set things up for a push start , told the guys where they could push and within a n arms length the car was running ! We had a good laugh about they thought they would have to push it a long distance . Once I figured out how to charge an 8 volt battery and probably repaired a sticking brake light switch push starting became few and far between .
alexiskai
Well-known member
The diode cutout is the secret ingredient. With a diode, the only requirement is that the generator be putting out a higher voltage than the battery, so if the battery is dead, the generator will be powering the car from the instant it starts spinning.
In experiments with a coil tester and a digital power supply, I was able to get good coils to fire pretty consistently at 4.1V. That wouldn't be enough to operate under load, but to just get the engine firing it would probably suffice.